1. Field of the Invention
The present invention relates to a titanium alloy tappet for use with valve systems in vehicles such as motorcycles, a method of manufacturing the titanium alloy tappet, and a jig effectively used in the method of manufacturing the titanium alloy tappet.
2. Description of the Related Art
For four-wheeled vehicles and two-wheeled vehicles, attempts have been made to clean an exhaust gas, reduce a noise, and achieve a high power output and low fuel consumption.
In order to achieve the high power output and the low fuel consumption, it is essential to equip lightweight components in the vehicles. To be specific, lightweight components of an engine or the like, for example, tappet for use with a valve system have been developed. The present applicant has already filed an application of an invention of the lightweight tappet (see Japanese Laid-Open Patent Application Publication No. 2000-327484). The conventional tappet that is made of steel is unable to be made thinner because its stiffness is decreased. Titanium alloy may be used because of its light weight and strength. However, the titanium alloy has a low sliding ability, i.e., a large friction coefficient, and tends to stick. If the titanium alloy is formed into a component adapted to slide at a high speed, for example, an engine speed of 15,000 rpm to 18,000 rpm, then sticking is more likely to occur. For this reason, it is difficult to replace the steel with the titanium alloy. In the above mentioned invention, the applicant made an attempt to apply a method of forming a DLC (diamond like carbon) film on a surface of the steel to reduce a friction resistance to the titanium alloy. But, the titanium alloy is incompatible with a forming process of the DLC film. Specifically, the titanium alloy is lower in adhesion strength with respect to the DLC film than the steel or other material, and therefore the DLC film is more likely to peel off from the surface of the titanium alloy after a short-time operation. Therefore, an improvement is needed to form the DLC film on a slidable portion made of the titanium alloy.